In applications involving dense bus ducts in corrosive environments, coating treatment requires a systematic design tailored to the environmental characteristics. Corrosive gases, salt spray, and chemical solvents accelerate the oxidation reaction between the metal casing and the conductor, leading to increased contact resistance, decreased insulation performance, and even structural failure. Therefore, the coating system must balance corrosion resistance, mechanical strength, and electrical insulation requirements, forming a multi-layered protective barrier.
The choice of casing material is fundamental to coating treatment. In highly corrosive environments, traditional galvanized steel or aluminum alloy casings are insufficient for long-term use, necessitating the use of corrosion-resistant materials such as 316L stainless steel. These materials contain molybdenum, significantly enhancing resistance to pitting and crevice corrosion. If ordinary carbon steel is chosen due to cost or processing limitations, a zinc layer must be formed through hot-dip galvanizing, utilizing zinc's sacrificial anodic protection to delay substrate corrosion. For extreme environments, an epoxy zinc-rich primer can be applied over the galvanized layer to further enhance protection.
The coating system should follow a composite structure of "primer-intermediate coat-topcoat." Primers need to possess strong adhesion and rust-preventive properties, such as epoxy zinc phosphate primers, whose phosphate components can form chemical bonds with the metal surface while providing cathodic protection. Intermediate coats often use epoxy micaceous iron oxide paints, whose flake-like structure can extend the penetration path of corrosive media and enhance the coating's shielding effect. Topcoats need to be selected based on environmental characteristics. Fluorocarbon coatings (PVDF), due to their fluoropolymer segments, have excellent chemical resistance, weather resistance, and self-cleaning properties, with salt spray tests exceeding 2000 hours, making them suitable for coastal or chemical industrial areas.
Special environments require targeted adjustments to the coating formulation. In petroleum refining environments containing hydrogen sulfide, the coating must have resistance to hydrogen embrittlement; modified epoxy coatings can be used, as the aromatic rings in their molecular structure can inhibit hydrogen atom penetration. For acidic gas environments, polysiloxane coatings, due to their silicon-oxygen bonds, exhibit stability against media such as sulfur dioxide and chlorine, while maintaining surface hydrophobicity and reducing the adhesion of acidic substances. In high-temperature and high-humidity areas, silicone-modified acrylic coatings can form a heat-resistant elastic film, adapting to thermal expansion and contraction caused by sudden temperature changes.
Protection of connection points is a weak link in coating treatment. Fasteners such as bolts and nuts require Dacromet coating; this process, through the synergistic effect of zinc flakes and chromates, provides high corrosion resistance without the risk of hydrogen embrittlement. For conductor lap surfaces, copper conductors easily form a cuprous oxide film in humid environments, leading to increased contact resistance. Tinning is necessary to form a tin protective layer, or silver plating can be used to improve conductivity and corrosion resistance. Aluminum conductors require anodizing to form a dense alumina film, blocking direct contact with corrosive media.
The application process has a decisive impact on coating performance. The substrate surface treatment must meet the Sa2.5 grade sandblasting standard to remove oxide scale and rust, ensuring coating adhesion. The coating environment must be controlled at a temperature of 5-40℃ and humidity below 85% to avoid coating runs or pinhole defects. When applying multiple layers of coating, ensure each coat is fully dry before applying the next to prevent a decrease in interlayer adhesion. For irregularly shaped structures or corner areas, use brush or spray application for touch-ups to ensure uniform coating thickness.
Regular maintenance is crucial for extending coating life. In corrosive environments, dense bus ducts should be visually inspected every six months, focusing on areas with blistering, peeling, or discoloration. Minor damage can be repaired locally with touch-up paint; however, if the damaged area exceeds 10%, complete rework is required. Simultaneously, maintenance cycles should be dynamically adjusted based on environmental monitoring data, such as salt spray concentration and humidity changes, to ensure the coating remains in an effective protective state.
